It has been discovered that the medical outcome for a patient suffering from severe brain trauma or from ischemia caused by stroke or heart attack or cardiac arrest is improved if the patient is cooled below normal body temperature (37° C.). Furthermore, it is also accepted that for such patients, it is important to prevent hyperthermia (fever) even if it is decided not to induce hypothermia. Moreover, in certain applications such as post-CABG surgery, it might be desirable to rewarm a hypothermic patient.
As recognized by the present application, the above-mentioned advantages in regulating temperature can be realized by cooling or heating the patient's entire body using a closed loop heat exchange catheter placed in the patient's venous system and circulating a working fluid such as saline through the catheter, heating or cooling the working fluid as appropriate in an external heat exchanger that is connected to the catheter. The following U.S. patents, all of which are incorporated herein by reference, disclose various intravascular catheters/systems/methods for such purposes: U.S. Pat. Nos. 6,881,551 and 6,585,692 (tri-lobe catheter), U.S. Pat. Nos. 6,551,349 and 6,554,797 (metal catheter with bellows), U.S. Pat. Nos. 6,749,625 and 6,796,995 (catheters with non-straight, non-helical heat exchange elements), U.S. Pat. Nos. 6,126,684, 6,299,599, 6,368,304, and 6,338,727 (catheters with multiple heat exchange balloons), U.S. Pat. Nos. 6,146,411, 6,019,783, 6,581,403, 7,287,398, and 5,837,003 (heat exchange systems for catheter), U.S. Pat. No. 7,857,781 (various heat exchange catheters).
Present principles understand that accurately and constantly measuring patient core temperature for feedback purposes and, maximizing the rate of cooling for therapeutic purposes are among the challenges posed by intravascular temperature control. Accurate patient core temperature measurements can be provided by rectal probes, esophageal probes, bladder probes, and the like but such probes are uncomfortable for awake patients. Placing a sensor on the catheter itself in a vein of the patient avoids the need for an uncomfortable separate probe but since the catheter changes the temperature of the blood flowing past the catheter, to avoid the “thermal shadow” of the hot or cold catheter, cooling or heating of the patient periodically must be temporarily suspended long enough for the temperature of the blood near the sensor to stabilize at actual core body temperature. This undesirably prolongs cooling, for instance, when it is desired to cool the patient.
As to maximizing the rate of cooling, the larger the heat transfer area of the catheter, the faster it can cool, but size limits are reached even when using the entire inferior vena cava as a placement site. Existing catheters must accommodate the vein into which they are placed. With the above recognitions in mind, present principles are provided.